The present invention relates generally to multi-component spraying systems and, more particularly, to air-assisted, airless-atomization, plural component spraying systems and methods.
Multi-component spraying systems have been used, for example, in manufacturing plastic articles by applying resinous materials to a mold or preform for an article. In such systems, a liquid resin and a catalyst for the resin are formed into spray particles directed to a substrate where the catalyst and resin react and harden to form the article. In such applications, the resin and catalyst components are preferably mixed together; and the mixture is sprayed onto the substrate. For example, in manufacturing articles with polyester resin, a catalyzing agent for the polyester resin is mixed with the resin; and the resin-catalyst mixture is applied to the substrate. In internal mix systems, the resin and catalyst are mixed within the spraying apparatus; and the mixture is atomized by a spray nozzle and directed onto the substrate. In external mix systems, the resin and catalyst are mixed externally of the apparatus after the resin and catalyst have been atomized. In both external mix and internal mix systems, complete and thorough mixing of the resin and catalyst is important to avoid non-uniform hardening of the resin on the substrate and other undesirable results. Multi-component materials have also been used, for example, in the manufacture of insulating foams by mixing and spraying the components of a foam-producing combination onto a substrate where they produce a hardened foam-like coating. More recently, multi-component painting systems have been developed that include plural components that react, when mixed, to form hardened decorative and protective coatings. Multi-component spraying systems have thus a multiplicity of applications, each with its specific requirements.
In many spraying systems, large quantities of pressurized air are used to atomize the liquid components. Such systems are expensive to operate and have a number of operational inadequacies. It is expensive to compress air, and the large quantities of compressed air used by existing systems impose a significant operating cost on the system. In addition, the blast of compressed air used to atomize the liquid components carries a significant quantity of spray particles away from the substrate, wastes the expensive material, creates an unclean spray area and generally requires overspray collection systems and contributes to the problem of operating such manufacturing operations safely. Furthermore, the use of large quantities of air during operation of the system can often create an undesirable spread of fumes.
In order to overcome some of the inadequacies attending the use of pressurized air to atomize components dispensed from a spraying apparatus, spraying systems have been developed which incorporate airless atomization techniques.
In prior airless atomization devices, an airless spray nozzle has been used to atomize liquid materials which are pumped at high pressure, that is, pressures generally exceeding 500-600 psi and more frequently in excess of 800 psi, typical operating pressure being 1000-1500 psi. The most commonly used airless nozzle includes an internal, hemispherical passage termination which is cut through by an external, V-shaped groove to form an elongated, elliptical-like orifice. Liquid material pumped at high pressures through such a spray nozzle is forced by the hemispherical termination of the passageway to converge in its flow at and through the elongated orifice. Because of the converging flow at the orifice, the liquid material is expelled through the orifice into a planar, expanding, fan-like film which breaks into spray particles which are carried by their momentum to the article target.
With viscous fluids, high pressures of 1000-1500 psi are required. Such high operating pressures impose a strain on system components reducing their reliability, require generally expensive components in the fluid delivery systems and contribute to the problem of operating such systems safely. Even at high pressures, however, such fan-like films, because they are formed by the convergence of the fluid, include heavy streams at the edges of the planar, fan-like film, which are referred to as "tails". Because of the heavy streamlike flow in the tails, the spray pattern formed by these edge portions of the expanding, fan-like film includes a disproportionate quantity of material and produces a non-uniform deposit with stripes when the spray pattern is swept across a substrate by a spray gun operator. The non-uniform deposit and resulting stripes make the blending of deposited material into a film of uniform thickness virtually impossible.
Past efforts to solve the problem of the tails attending the use of airless spray nozzles have included the insertion of a "preorifice" immediately behind the elongated, elliptical-shaped orifice to concentrate a greater portion of the flow in the central portion of the fan. Although preorifices are helpful, they are not completely satisfactory, adding another source of clogging to the spray gun and another variable factor to be integrated into system operation.
Compressed air has also been used to solve the problem of tails created by airless spray nozzles. See, for example, U.S. Pat. No. 3,202,363; 3,521,824; 3,635,400; 3,843,052; and 4,386,739 and Japanese patent publication No. 57-90762. In plural component spraying systems, compressed air has been used to assist in the atomization of plural component materials as shown, for example, in U.S. Pat. Nos. 2,780,496; 2,864,653; 3,799,403; and 4,618,098 and British patent specification No. 735,983.
External mix plural component systems originally included a plurality of separated spray gun or spray nozzles that were directed to blend their patterns together and to mix thereby resins and their catalysts or hardening agents. See, for example, U.S. Pat. Nos. Des. 252,097; 3,893,621; 4,123,007; 4,618,098; and 4,713,257.
In prior art external mix, plural component spraying systems using airless resin nozzles, catalyst spray has been injected into the resin spray formed from an airless spray nozzle at distances on the order of one inch or more in front of the airless spray nozzle. This downstream location for insertion of the catalyst spray provided mixing of the catalyst spray particles with resin spray particles which had already been formed from the liquid resin at this location. In such prior plural component systems, resin spray particles are formed within a fraction of an inch of the airless spray nozzle, either under the influence of high hydraulic resin pressures, typically on the order of 1000 psi, or the combined action of lower hydraulic resin pressures and a plurality of compressed air jets located adjacent the airless resin nozzle and directed at the expanding fan-like resin film directly adjacent the liquid orifice of the resin nozzle. Introduction of the catalyst to the spray more than an inch downstream of the liquid orifice was to avoid the collection of catalyst on the resin nozzle, among other things. An accumulation of catalyst on the resin nozzle will combine with resin at the resin nozzle orifice and cure the resin, blocking the resin nozzle orifice and requiring removal of the resin nozzle for cleaning or replacement.
In such prior external mix systems, a substantial flow of air accompanied the rapidly moving resin particles at the downstream location of catalyst injection; and this substantial flow of air was transverse to the direction of the catalyst spray being injected into the spray pattern and made it difficult to inject catalyst particles uniformly into the resin spray. In addition, in such prior external mix systems, the catalyst particles were injected by the associated apparatus into a flow of compressed air that was directed to blow the catalyst particles into and mix them with the resin spray particles. The flows of air accompanying the formation of the resin particles and used to blow the catalyst particles into the resin spray produced uncontrolled billowing air movements which prevented the fine catalyst particles from being incorporated into the spray pattern and being mixed with the resin particles and deposited on the substrate. Importantly, the air flows associated with such prior external mix systems led to the escape of fine catalyst particles into the surrounding environment, thus presenting cleaning problems and requiring air removal systems.
Furthermore, in such prior external mix systems, it was difficult to obtain desirable spray patterns. The use of the plurality of compressed air jets to assist in atomization of the expanding resin film directly adjacent the liquid orifice of the airless nozzle, where the film had substantial integrity, resulted in a deflection of a portion of this compressed air and contributed to the uncontrolled billowing. This was especially true in systems in which the compressed air jets were directed against the airless nozzle itself. The focus of the compressed air jets at the airless resin nozzle to assist atomization of the resin film made it difficult to form resin and catalyst particles into a desirable spray pattern. Furthermore, because of the direction and force required of the compressed air to carry the catalyst particles into the resin spray more than an inch in front of the resin nozzle and to achieve mixing of the catalyst particles with resin particles substantially downstream of the resin nozzle, the compressed air used to entrain the catalyst particles was not effectively used to provide a satisfactory spray pattern.
Moreover, plural components spraying methods and apparatus have been encumbered by the use of large spray guns attached to a plurality of hoses. Such guns were heavy, and their manipulation was resisted by a plurality of hoses attached at various locations to the spray gun body. While the weight and dimensions and the inability to manipulate, by twisting and turning, the spray guns was no more than an inconvenience in the application of plural component materials to such large items as boats, shower stalls, roofs and the like, which are characterized by very large, relatively planar surfaces, they limited the applicability of the prior plural component spraying systems and apparatus to industrial painting applications in which a workman must frequently twist and turn the gun in all directions while holding it at arms length, and must frequently insert it into cavities and recesses formed in manufactured objects. These prior plural component systems and apparatus were, at least, commercially unattractive for industrial painting applications and, in many cases, unusable.